When an image forming apparatus for an area where the commercial power supply voltage is a 100 V system (for example, 100 V to 127 V) is used in an area where the commercial power supply voltage is a 200 V system (for example, 200 V to 240 V), the maximum power that can be supplied to a heater of a fixing part (fixing device) of the image forming apparatus becomes four times as large. If the maximum power that can be supplied to the heater increases, harmonic currents, flickers, and the like generated in electric power control of the heater such as phase control or wave number control become conspicuous. In addition, because the electric power generated when the fixing device exhibits thermal runaway without normal operation increases by four times, it is necessary to have a safety circuit with quicker response. Therefore, when the same image forming apparatus is used in areas where the commercial power supply voltage is 100 V and where the commercial power supply voltage is 200 V, it is common to use individual heaters having different resistance values for the respective areas by replacement.
On the other hand, as means for realizing a universal apparatus that can be used in both areas where the 100 V commercial power supply voltage is supplied and where the 200 V commercial power supply voltage is supplied, there is proposed a method involving switching the resistance value of the heater using a switching unit such as a relay. In Patent Literatures 1 and 2, there is proposed an apparatus that can be used in both areas where the commercial power supply voltage is 100 V and where the commercial power supply voltage is 200 V. The apparatus includes a first heat generating member and a second heat generating member, and can switch between a first operating state in which the first heat generating member and the second heat generating member are connected in series and a second operating state in which the first heat generating member and the second heat generating member are connected in parallel, thereby switching the resistance value of the heat generating member according to the commercial power supply voltage.